In the manufacture of semiconductor devices and other products, ion implantation systems are used to implant dopant elements into workpieces (e.g., semiconductor wafers, display panels, glass substrates). These ion implantation systems are typically referred to as “ion implanters”.
Absent countermeasures, during the ion implantation process, energy can build up on the workpiece in the form of heat as the charged ions collide with the workpiece. This heat can warp or crack the workpiece, which may render the workpiece worthless (or significantly less valuable) in some implementations.
In addition, even if the workpiece is not rendered worthless, this undesired heating can cause the dose of ions delivered to differ from the dosage desired, which can alter the functionality from what is desired. For example, if a dose of 1×1017 atoms/cm3 are desired to be implanted in an extremely thin region just below the outer surface of the workpiece, unexpected heating could cause the delivered ions to diffuse out from this extremely thin region such that the dosage actually achieved is less than 1×1017 atoms/cm3. In effect, the undesired heating can “smear” the implanted charge over a larger region than desired, thereby reducing the effective dosage to less than what is desired. Other undesirable effects could also occur.
In other instances it might be desirable to implant at a temperature below ambient temperature, to allow for desirable amorphization of the silicon wafer surface enabling ultra shallow junction formation in advanced CMOS integrated circuit device manufacturing.
For these and other reasons, cooling systems have been developed to allow the chuck to be cooled to very low temperatures. Although cooling systems are known in some respects, such as in plasma processing apparatuses, it is extremely difficult to integrate a vapor cooling system into an ion implanter due to the mechanical density of components near the workpiece. For example, electrostatic chucks in ion implanters are often considerably more complicated that those used in less complicated plasma processing apparatuses. The inventors have developed techniques and systems for cooling electrostatic chucks in ion implantation systems, which can reduce undesired heating of workpieces undergoing implantation. Other methods for cooling an electrostatic chuck could comprise circulating a chilled fluid through the chuck at roughly, or slightly below, the temperature desired for implant.